Pre-debut The members of Billlie were known as Mystic Rookies — a rookie development program under
Mystic Story. On September 14, Mystic Story announced plans to debut Mystic rookies in November 2021. On October 11, it was revealed that the group would be named 'Billlie'. Prior to debut, Moon Sua was a
YG Entertainment trainee for 10 years. She participated in the music competition program
Unpretty Rapstar 2 finishing as the third runner-up. Suhyeon participated in the
Mnet survival program
Produce 101 placing 69th and eliminated in the fifth episode. She also participated in the
JTBC survival program
Mix Nine and starred in the web drama
A-Teen in 2018, and its 2019 sequel
A-Teen 2. Haram and Tsuki are former
SM Entertainment trainees. Sheon participated in the
Mnet survival program
Girls Planet 999, and was eliminated in the final episode placing tenth. Siyoon participated in the talent show
K-pop Star 5 and also worked as a model for the magazine
Popteen. On November 10, their debut EP
The Billage of Perception: Chapter One was released featuring lead single "Ring X Ring" and five B-side tracks. On November 19, it was announced that Kim Su-yeon, who had participated in
Girls Planet 999, would join the group under the stage name Sheon (션) as the seventh member, and would officially join the group for their next album. On November 27, Sheon made a surprise appearance performing title track "Ring X Ring" along with the other members on South Korean music show
Show! Music Core, marking her first appearance with the group. On December 14, the group released their first digital
single album The Collective Soul and Unconscious: Snowy Night with "Snowy Night" as the lead single. The single is the group's first release to feature member Sheon. On February 11, 2022, it was announced that Billlie would be releasing their second EP
The Collective Soul And Unconscious: Chapter One, featuring lead single "GingaMingaYo (The Strange World)" on February 23. On March 1, the group released their first soundtrack album
The Collective Soul and Unconscious: Chapter One Original Soundtrack from "What Is Your B?". On August 8, it was announced the group would be releasing a direct
sequel to their first EP. On August 16, it was announced that their third EP
The Billage of Perception: Chapter Two, featuring lead single "
Ring Ma Bell (What a Wonderful World)", would be released on August 31. On February 7, 2023, it was announced the group would be releasing their fourth EP. On March 6, it was announced that their fourth EP
The Billage of Perception: Chapter Three, featuring lead single "Eunoia", would be released on March 28. On April 20, Mystic Story announced that the group's activities have been halted, due to the sudden death of Moon Sua's brother
Moonbin of
Astro. Subsequently on April 25, Mystic Story announced that promotions for the EP have concluded, and that member Moon Sua would be taking time off, with the remaining 6 members to continue activities. On June 15, It was announced that Suhyeon would also be going on hiatus, for health reasons. The group released their first single album
Side-B: Memoirs of Echo Unseen. The album's single "BYOB (Bring Your Own Best Friend)", together with its English-language version, was pre-released on September 27. The lead single "Dang! (Hocus Pocus)", together with the entire album was released on October 23. Members Moon Sua and Suhyeon would not be involved in this release due to their hiatuses from health issues.
2024–present: First sub-unit and first studio album On April 12, 2024, it was announced that members Moon Sua and Suhyeon would resume activities after being on hiatus due to health issues. On October 2, it was announced that the group would be releasing their fifth EP
Appendix: Of All We Have Lost on October 16, with the pre-release single "Trampoline" releasing on October 11. The music video teaser for the lead single "Remembrance Candy" () includes a special narration by singer-songwriter
IU, who also wrote the lyrics for the song. On April 1, 2025, the group announced that they would debut their first sub-unit consisting of members Moon Sua and Siyoon on April 7, with the release of the single "Snap" featuring
Sokodomo. On January 19, 2026, it was announced that Billlie would release a pre-release single titled "Cloud Palace (False Awakening)" on January 27, ahead of their upcoming album
The Collective Soul and Unconscious: Chapter Two. On April 15, the album was announced to be released on May 6 as the group's first studio album. ==Members==